1. Field of the Invention
The present invention concerns a device for an electrophotographic apparatus and, more specifically, a device for detecting the presence of a developing unit and the toner level contained in the developing unit.
2. Background Art
Monitoring the presence of a developing unit and the level of toner of the cartridge is crucial for the proper operation of an electrophotographic apparatus during the printing process. An electrophotographic apparatus can be either one of a laser printer, an electronic copier, a facsimile machine, or any versatile office machine. The general operation of an electrophotographic apparatus starts with paper being loaded as from a supply tray and then transported through to a high pressure transfer unit. The high pressure transfer unit places the toner image onto the sheet of paper. Subsequently, the paper is transported to a fixing device that fixes the toner image onto the paper using both heat and pressure rollers.
To prepare the toner image for the high pressure transfer unit, it is necessary to attach toner particles to the latent electrostatic image on the photoconductive drum. The toner particles are applied by a the developing unit, thereby transforming the latent electrostatic image into a latent toner image. Thus, the level of toner in the developing unit is critical to the proper operation of the electrophotographic apparatus. This importance has lead to many developments in toner detection methods. By way of example, U.S. Pat. No. 5,436,704 to Moon entitled Device for Sensing the Amount of Residual Toner of Developing Apparatus, mentions using a reed switch in combination with an magnet bearing actuator to determine the amount of toner remaining in a developing unit, and U.S. Pat. No. 5,428,427 to Lee entitled Device for Detecting Toner Used in an Electrophotography Machine, shows a device employing a magnet to determine whether fresh toner needs to be supplied to the developing unit. Some other patents representative of the art are: U.S. Pat. No. 5,095,331 to Takano entitled Image Forming Apparatus Having Toner-Empty Detecting and Indicating Mechanism; U.S. Pat. No. 4,951,091 to Nawata entitled Image Forming Apparatus Having Toner Quantity Detection Means; and U.S. Pat. No. 4,739,365 to Hino entitled Developing Unit for an Electro-Photographic Apparatus.
I have observed that the electrophotographic apparatuses in the art require an additional detector to determine the presence of a developing unit as well the level of toner in the developing unit. The use of two detectors increases the complexity of assembly and correspondingly increases the cost of the electrophotographic apparatus. I expect that a device that both determines whether a developing unit is present in an electrophotographic apparatus and whether the toner needs to be replaced will increase the efficiency of manufacture of electrophotographic apparatus and lower the cost of production.